1. Field Of The Invention
This invention relates to the determination of flow rates of well fluid constituents, and more particularly, to a method and apparatus where such determination is made by taking and extrapolating measurements of a sample fluid stream rather than directly measuring the total fluid stream.
2. Description Of The Prior Art
After an oil or gas well has been drilled, it is necessary and desirable to determine the flow rates of the various constituents of the well fluid. For example, in a "three-phase" well fluid, these constituents are oil, gas and water.
In previous testing, a fluid stream is flowed from the well through a surface test tree at the wellhead into a processor. This fluid stream is throttled through a choke manifold, but a fairly large fluid stream is required to insure that the constituents of the fluid stream are representative of those in the well. The fluid stream is generally flowed into a heater and separator in the processor, both sized to accommodate the appropriate flow. The separator separates the fluid into its gas, oil and water constituents. The separated constituents are flowed out of the separator in individual lines. The flow rate of the constituent in each line is measured, so that the operator will know the relative amounts of each. After these measurements are made, the liquid constituents may be recombined into a single line and the gas constituent flared. The single liquid line may be flowed into an test tank in which a total flow rate may be determined for insuring proper calibration of the individual flow meters. The fluid is then pumped to a burner where it is eliminated.
A problem with this prior art method is that it requires the heater, separator, meters, test tank and pump to be sized to accommodate the total fluid flow from the wellhead. Obviously, this also requires the appropriately sized piping and fittings in the processor. Such equipment is relatively expensive, and the size of it requires a great deal of rig space. Space is at a particular premium on offshore drilling rigs. Transportation of such large equipment is also fairly expensive because of its weight and bulk.
An additional problem with prior processors used in determining the flow rate of well constituents is that the pressure vessels, such as the separator and test tank, usually must be of a size that requires certification under the American Society of Mechanical Engineers Boiler and Pressure Vessel Test Code.
Accordingly, there is a need for a test method and apparatus which utilizes smaller and lighter equipment to save on rig space and transportation problems. Additionally, it is desirable to have tanks small enough that they fall below the requirements of ASME specifications. Of course, these reductions in size would also greatly reduce the cost of the apparatus. The present invention addresses these needs by providing a method and apparatus which may be used for determining the flow rates of well constituents on a much smaller scale than previously known equipment.